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Two-way Radio Breakthrough To Double Wi-Fi Speeds
An anonymous reader writes "Scientists at Stanford University have built a radio that can transmit and receive at the same time on the same frequency. The breakthrough could lead to a twofold increase in performance for home wireless networks and end that annoying habit of pilots finishing every sentence with 'over.'" But you can still do it if you like. I'm not judging.
First post, Over.
Doing this On the same frequency is remarkable. but the gains they are claiming can be had right now by using TWO frequencies. Transmit on channel 1 receive on channel 12.. the other end does the opposite. the thing is, 90% of Ethernet traffic is not bi directional. it's packetized so their claims of DOUBLE will not be realized. when you set up a network connection from half duplex to full duplex you do not see a double in speed, just a double in capacity.
Do not look at laser with remaining good eye.
We say over or have a tone to signify when we are done speaking. There may be more than one person listening and its a cue for the next person not only that you are done talking, but your message came through. If you are listening and don't hear "over" or "beep" you say "come again" or "missed that last bit" or whatever jargon that the bands you are using requires. I'm not a pilot so all I know is terms i've used on CB over the years.
Roger Murdock: Flight 2-0-9'er, you are cleared for take-off.
Captain Oveur: Roger!
Roger Murdock: Huh?
Tower voice: L.A. departure frequency, 123 point 9'er.
Captain Oveur: Roger!
Roger Murdock: Huh?
Victor Basta: Request vector, over.
Captain Oveur: What?
Tower voice: Flight 2-0-9'er cleared for vector 324.
Roger Murdock: We have clearance, Clarence.
Captain Oveur: Roger, Roger. What's our vector, Victor?
Tower voice: Tower's radio clearance, over!
Captain Oveur: That's Clarence Oveur. Over.
Tower voice: Over.
Captain Oveur: Roger.
Roger Murdock: Huh?
Tower voice: Roger, over!
Roger Murdock: What?
Captain Oveur: Huh?
Victor Basta: Who?
A bad analogy is like a leaky screwdriver.
How this actually works :
The Challenge in Achieving Full-Duplex
The problem that has historically prevented full-duplex is that, when a node transmits, its own signal is millions of times stronger than other signals it might hear: the node is trying to hear a whisper while shouting. The challenge is canceling the node's own transmitted signal (shout) from what it receives (whisper). Existing approaches, such as digital cancellation and noise cancellation circtuis, can cancel some of the transmitted signal, reducing its strength, but not enough to make a node able to receive.
Antenna Cancellation
Our design uses two transmit antennas one receive antenna per node. The transmit antennas send the same data and the receive antenna is placed such that there is destructive interference from the two transmit antennas, thus reducing self-interference. Offsetting the two transmit signals by half of the wavelength causes them to cancel each other, creating a null position where the transmitted signal is much, much weaker.
Combining antenna cancellation with cancellation through a noise cancellation circuit gives ~50dB reduction in self-interference before the RF signal is demodulated and sampled to the digital domain. Digital cancellation removes the residual interference.
For more information :
http://sing.stanford.edu/fullduplex/
The actual paper (PDF) :
http://sing.stanford.edu/pubs/mobicom10-duplex.pdf
I end all my sentences with *ksschk* so it sounds like I'm in space.
It's called time domain multiplexing. If you chop the transmitter on and off at a rate much faster than the data rate you can hear bits in between your chopped up transmissions. Sorta like fast break-in amateur CW where you can hear between the dots and dashes. This would require synching the two stations chop rate. Since the 'chopping' is done above the nyquist sample rate, no data is lost, and you get true full duplex speed.
No it doesn't, I hope you don't fly anymore you're making a careless mistake about something that should have been taught to you before you took the ground exam.
The purpose of an End of Transmission marker is so that everyone listening has confirmation that they received ALL of your transmission as intended. So if for some reason my transmission is cut off and it seems like just silence you as a listener know it was cut off because you didn't hear an End of Transmission marker and you can request that it be repeated.
If you think 'silence' is the way to tell, you don't need to be anywhere in an aircraft except the passenger cabin, there are a ridiculous number of airline accidents that result because of just this sort of stupidity, a fine example is a Pan-Am flight which started a takeoff roll after knowing they didn't get a full transmission from the tower ... which told them to hold until another aircraft which had to taxis back up the runway itself could clear it. About 500 people died that day because some idiot thought silence was good enough and ignored procedure which would have been to ask for a repeat. Half way down the run way, as their 747 approached rotation speed, out of the fog appeared another jumbo jet, turning off the runway right in front of them. All because they knowingly didn't follow preceedure and ask for a repeat when the cockpit voice recorder clearly shows them noticing, pointing out, and ignoring the missing End of Transmission marker.
The click when you release the mic is there because idiots like you couldnt' follow procedure so they took it out of your hands in order for everyone else that actually has a clue to be safer. Either way, your lack of understanding of why procedure is the way it is gives me a very disturbing feeling.
Persistent Volume manager for Kubernetes - https://github.com/dwimsey/openshift-pvmanager
The signals will only perfectly cancel when they are separated by a distance that is exactly one half the wavelength. Assuming you separate the two transmit antennas by this distance at the carrier frequency, then there will be a limitation on the available bandwidth. This is because the further you get away from center frequency, and away from the ideal antenna spacing, the less destructive interference you will have (and the more your transmit signal will leak into your receive signal). So you will double your capacity for only narrowband channels.
The pdf gives actual numbers. I just wanted to point out that there is a limitation on bandwidth.
You might also think, "If I know what I'm transmitting, why can't I just subtract it from what I receive?" This has to do with the dynamic range of the receiver, which is a function of the number of bits in your analog to digital converter. You must attenuate your received signal so that you don't saturate your converter. Have you ever turned the volume up so loud that you begin to hear distortion? It's the same thing.
So you are receiving this loud unwanted transmit signal, and this soft receive signal. You must lower the volume so that you are not distorting the highest signal. This lowers the volume on the desired signal as well. You can lower it so much that your analog to digital converter is not able to differentiate between a 1 and a 0 anymore.
I think if you could have an A2D with enough bits that you didn't care if you received the transmitted signal, then you could just carefully subtract out the unwanted transmit signal. Maybe I should patent that? Meh. I'm probably wrong.
The researchers have not detailed when the technology might appear in hardware, but said they had applied for a patent and ...
So....never?
Sorry to break it to you, but your grandma didn't have a magic modem. On a plus side, she probably wasn't a witch either.
http://en.wikipedia.org/wiki/56_kbit/s
A 56 kbit/s line is a digital connection capable of carrying 56 kilobits per second (kbit/s), or 56,000 bit/s, the data rate of a classical single channel digital telephone line in North America. In many urban areas, which have seen wide deployment of faster, cheaper technologies, 56 kbit/s lines are generally considered to be an obsolete technology.
The figure of 56 kbit/s is derived from its implementation using the same digital infrastructure used since the 1960s for digital telephony in the PSTN, which uses a PCM sampling rate of 8,000 Hz used with 8-bit sample encoding to encode analogue signals into a digital stream of 64,000 bit/s.
However, in the T-carrier systems used in the U.S. and Canada, a technique called bit-robbing uses, in every sixth frame, the least significant bit in the time slot associated with the voice channel for Channel Associated Signaling (CAS). This effectively renders the lowest bit of the 8 speech bits unusable for data transmission, and so a 56 kbit/s line used only 7 of the 8 data bits in each sample period to send data, thus giving a data rate of 8000 Hz × 7 bits = 56 kbit/s.
See also here:
http://en.wikipedia.org/wiki/56_kbit/s_modem#Speed
Like 10 years ago, there was a period of a few weeks where, by some random bug or glitch somewhere, my grandmother's computer (with 56k modem) would regularly connect to her dial-up service at 118.2kbps. She, of course, never noticed it. I don't think anyone else did, either. I noticed it when my parents and I went over to visit, and I asked to use the computer because I was bored.
Let me guess... Windows 98?
That was a common bug back then. Probably something to do with all that 16-bit and 32-bit code just thrown on the pile there.
You were probably connecting way bellow even 56k, it's just that you couldn't really notice it.
Also, it could simply be that her PC was reporting the port speed, not the actual speed it connected at.
Even XP will gladly report to you the speed of your NIC or your hub/switch/router instead of your actual internet connection speed.
Mit der Dummheit kämpfen Götter selbst vergebens
Because in any case, the pilot has finished his/her message when you hear the mic click. Surely you don't think the conversation is going to continue?
More importantly, the pilot and controller speak to each other in very precisely defined and very concise language. It's pretty obvious when one of them is done yakking, the mic click is a convenience, like the "over" used to be before all radios had mic clicks.
A typical initial approach might go something like this:
"Bangor approach, Cessna five-two-five-Lima-Charlie, 12 miles west, descending 5000 with information Sierra, full stop."
This tells the controller that:
1. You are intending to make an announcement to the controller at Bangor Center in charge of approaches (in case you fucked up your frequency, they can correct you quickly and get you on the right frequency).
2. You are a Cessna, US-registered, with tail number N525LC.
3. You are 12 miles to the west of the airport, at 5000 feet, and descending.
4. You have listened to their weather/conditions report recently, which is their update "S" (Sierra), and the letter is updated whenever the information is updated (usually once an hour). That means you already know the wind speed, altimeter settings, and preferred runway, and have adjusted all of your instrumentation and expectations appropriately.
5. You are requesting approach vectors for the currently-active runway (which you already know) and you intend to land there (full stop, as opposed to a touch-and-go or a practice approach but not a landing).
The controller will respond with something like this:
"Cessna Five-Lima-Charlie, Information Sierra current, enter 45 left downwind for runway one-eight-zero, report midfield"
This means:
1. The controller has acknowledged your presence, confirmed that you have the latest weather, and picked an abbreviation for your tail number that does not conflict with any other aircraft currently operating in his airspace. That will be your designation for the duration of your talk with this controller.
2. The controller wants you to enter the pattern at a 45-degree angle on the upwind side of the runway and call you again when you are properly established in a left downwind and abeam the middle of the runway.
3. There is no known traffic on that side of the field that will conflict with your entry, because the controller didn't mention any.
The conversation will proceed, with both the pilot and controller keeping radio use to the absolute minimum necessary to communicate what they need to say. If the frequency is really quiet, they might exchange a few jokes or snide remarks, but "over" is usually in the domain of CB radio, old timers who used to deal with really crappy radios, and bad movies.
Interruptions to what a pilot or controller is saying are obvious because of the way the language is constructed. This is done on purpose. If you say "Bangor approach, Cessna three-five..." then stop talking, you're going to hear a controller say something like "Unknown Cessna starting in three-five, please repeat, message not received." in just a very small handful of seconds.
"This post contains words, known to the State of California to cause thought. Wash brain thoroughly after reading."
It seems that in your rush to prove your superiority and brand me an idiot you missed the smiley, despite quoting it, possibly because it came after the End of Sentence marker and you'd stopped reading :P (There, did you get that one?) For the record, I haven't logged any flight time since summer 2000, so I'll grant you that my R/T is a little rusty, but I did know and use proper phraseology. I had to, or I'd get ritually humiliated by my colleagues in Air Traffic... Working at a commercial flight training centre, especially in one with "AREA OF INTENSE AERONAUTICAL ACTIVITY" plastered across it on the half-mill chart, you simply don't get away with sloppy R/T.
I love people who throw phrases like "idiots like you" around. Have to say I didn't especially enjoy sharing a cockpit with them, though, no matter how superior they thought they were. They tended to be precisely the sort of egotistical pillock that everyone but them knew was going to up in a smoking hole somewhere, and two I know of from flying elsewhere did just that. (Well, one in a smoking hole and one in a long line of aircraft parts across a mountain, since we're being pedantic.) A third disappeared behind the trees before recovering from his ill-advised attempt at aerobatics, I don't know how he survived.
I've flown as passenger and pilot with all sorts, from the late Mr. Cool to the chap who disabled the Bismarck (I saw the logbook entry) and a very quiet unassuming gentleman who turned out to have more types in his logbook than most of the instructors had hours. And I'll tell you this much: I'd far rather fly with the under-confident guy who's a bit mixed up on the R/T than the one who knows it all and thinks everyone else is an idiot. As my instructor said: The under-confident can learn, but the over-confident will. One way or another.
Correct. I last flew about two years ago. We don't say "over". Ever. You sound like a trucker on a CB and you're only going to piss off the tower and the other pilots on the freq because you're wasting airtime, and sound like you don't know what you're doing. ATC comms can get super busy, and lives are (literally) at stake. If you listen to even a Class C approach frequency, it will sound like a nearly uninterrupted stream during busy times of the day. There isn't time for extraneous nonsense when Cessna 241H is trying to declare a fuel emergency, or Southwest 2301 needs to expedite their climb. I know it sounds silly "what is the big deal with just saying 'over'?" but that is extra two syllables in every communication between pilot & controller or pilot & pilot which are totally superfluous.
It is superfluous because ATC comms have a cadence that makes it pretty clear when you're finished with a routine call. Pilots and controllers are both familiar with this cadence, so we know generally what information to expect from each other. This is what a typical sequence would sound like at a field in class D airspace:
P: Bolton Tower, Cessna niner five four seven whiskey
T: Cessna niner five four seven whiskey, Bolton Tower
P: Bolton Tower, Cessna niner five four seven whiskey over Lily Chapel, inbound for full stop
T: Cessna four seven whiskey, proceed inbound and report midfield right downwind for runway two two
P: Right midfield for 22, cessna four seven whiskey
...
P: Bolton Tower, four seven whiskey midfield downwind for two two
T: Four seven whiskey, you're number two behind the Baron on one mile final
P: Four seven whiskey, number two looking for traffic
P: Four seven whiskey has traffic in sight
T: Roger. four seven whiskey, cleared to land runway two two
T: Baron three foxtrot six, turn right on alpha four and contact ground point eight
B: Right on alpha four, ground point eight. good day
...
T: Four seven whiskey, turn right on alpha three and contact ground point eight
P: Right on alpha three, ground point eight. good day
That is a very normal,typical airspace entry and landing procedure. Even in an emergency, we don't use "over" - because again, time is critical and time wasted saying things that aren't needed is concentration and mental energy taken away from the pilot's number one job - flying the airplane.
There is very little future in being right when your boss is wrong.
>pilot and controller speak to each other in very precisely defined and very concise language
Nice example, thanks!
>CB radio, old timers who used to deal with really crappy radios, and bad movies.
Saying "over" is necessary when operating SSB on HF, you don't hear the mic clicks and sometimes not sure if person on other end has finished talking. Coast Guard uses "over" when operating on VHF marine channels which I assume for boat drivers steering outside or with a noisy engine or wind.
Bad movies don't use "over." They use "over and out."
mfwright@batnet.com